Freezing point depressant compositions are used widespreadly for variety of purposes, especially for lowering the freezing point of an aqueous system so that ice cannot be formed on surfaces or within the aquous systems or for melting ice formed in those aqueous systems.
The effectiveness of the freezing point depressant compositions depends on the molar freezing point lowering effect, the number of ionic species that are made available and to the degree to which the compositions can be dispersed in the liquid phase. Water is the most common liquid phase in which the formation of ice is to be precluded or ice to be melted. Most freezing point depressant compositions are either based on salts such as sodium chloride or potassium formate or alcohols such as glycols and methanol.
Oil based hydraulic and heat transfer fluids have negative environment impact and they also form a favorable growth environment for microbes, from which there results formation of precipitates, and corrosion. The mineral and vegetable oils (bio oils) as well as biodegradable and non-toxic propylene glycol based fluids have the disadvantage that their viscosities increase to detrimentally high values at low temperatures e.g. for the most hydraulic and heat transfer oils the typical operating temperature is only −10° C. Both ethylene and propylene glycol can operate at lower temperatures, even down to −30° C., but especially in case of propylene glycol the pumping costs increase remarkably because of the poor heat and power transfer properties. The viscosity of hydraulic and metal cutting fluids should be within range of 10-50 mPas or even higher. The viscosity should not be too low. If the viscosity is very low, for example in order of 1 mPas, simple o-ring seals have to be abandoned in hydraulic equipment and other more expensive options must be used. The low viscosity of metal cutting fluid will cause weakening of the metal surface quality in case of metal cutting. Bio oils and mineral oils are very sensitive to moisture (typically maximum ca. 0.1 wt-%) and high temperatures. Oils are not water soluble, thus water containing acidic and corrosive compounds from oil will concentrate at the bottom of equipment and cause extremely corrosive environment. Separate phases of oil and water will cause pumping problems also. High temperatures will cause danger for fire.
Alkali and alkali-earth metal salts of carboxylic acid such as potassium formate, sodium formate, potassium acetate and sodium acetate have found increasing use in the area of heat transfer and power transfer (hydraulic) and deicing mainly due to their low environment impact and low viscosity at minus temperatures. When using these formate and acetate based alkali and alkali-earth metal salts as heat transfer fluids, they can operate even at −40° C. without noticeable increase in the pumping costs. Corrosion is the drawback of these fluids. High electrical conductivity, over 200 mS/cm, and the tendency to form precipitates are the main reasons for the increased corrosion. Besides corrosion, the alkali and alkali-earth metal salts of carboxylic acid are prone to salting out and precipitate formation. Salt crystals formed at the cleavage of the pumps, on the inner surfaces of the nozzles may cause the whole heat transfer, hydraulic system or NOx catalyst system to collapse. Pumps start leaking or the nozzles simply clog and thus the fluid cannot pass through. And, the corrosion underneath the crystal precipitates is very severe.
The deicing and anti-icing fluids and these fluid containing compositions, which are used in the airports, have been traditionally formulated from ethylene glycol, propylene glycol, and urea. Ethylene glycols are toxic and thus require expensive treatment and disposal. More safer fluid such as propylene glycol and urea biodegrade too rapidly imposing excess oxygen demand on the environment or the sewage treatment plant. As a consequence, airports were forced to switch to deicers such as compositions comprising fluids based on potassium formate and potassium acetate to reduce biological and chemical oxygen demand. However, a number of airports and air line companies have reported severe corrosion problems with these compositions. Catalytic oxidation (corrosion) of aircraft carboncarbon composite brakes resulting from potassium formate and potassium acetate has become a major safety issue. Existing literature data has demonstrated that potassium, sodium, and calcium cations are responsible for the catalytic oxidation of carbon, not the formate or acetate anion itself. Furthermore, because potassium formate and potassium acetate have high electrical conductivities and they are prone to salting out i.e. to the salt precipitation over the metal surfaces they have detrimental corrosion effects on electrical connections within the air plane e.g. in the metal plates such as cadmium plated landing gear parts. In 2005 when, when one European airport switched from products based on urea and ethylene glycol to potassium formate based products, corrosion of zinc coated steel occurred on flight structures, as well as on maintenance and ground operation vehicles [ACRP Synthesis, Impact of Airport Pavement Deicing Products on Aircraft and Airfield Infrastructure, 7.1.2009, ISSN 1935-9187, ISBN 978-0-309-09799-4, 2008 Transportation Research Board].
Moreover, the synergistic generation of residue when aircraft anti-icing composition or fluid based on glycols is splattered with potassium formate or acetate runaway deicing fluid presents serious concerns about residue gel hydration and refreezing in flight and has produced potential dangerous rough residues on leading edge surfaces on aircraft. This can negatively affect in-flight handling of the aircraft if deposits occur on or near control surfaces or linkages. Initial research has shown that the thickener used in the aircraft deicer fluids will separate due to the contact with potassium formate or potassium acetate based runaway deicing fluids. [Hille, J., “Deicing and Anti-icing Fluid Residues,” Boeing Aero Magazine, 1st quarter, 2007, pp. 15-21].
In spite of the environmental advantages over the formulae such as urea and glycols, alkali-metal-salt based runaway deicer compositions such as compositions based on potassium formate and potassium acetate present potential problems both in deicing airplanes or airfield infrastructures and also in using to heat transfer as well.
Heat storage chemicals are typically based on hydrated fluoride-, chloride-, sulfate-, and nitrate salts or salt combination. These salts are quite harmful to environment and corrosive especially to light metals such as aluminum and magnesium used in modern auto industry or heat storage plants (e.g. solar heating and electrical heating on low tariff hours) that are areas that can benefits from non corrosive heat storage chemicals.
Other prior art freezing point depressants, such as ethanol and methanol, have toxic effects and high volatility. They are also a cause of offensive smell and fire danger.
U.S. Pat. No. 6,835,323 discloses an alkali metal, an alkaline-earth metal salt or an ammonium salt of formic acid for the device which hydrostatically transmit power.
U.S. Pat. No. 7,201,982 relates to a method for cooling an electrical system comprising circulating in a cooling system of the electrical system a mixture comprising a heat transfer fluid and one or more carboxylic acid salts thereof. The carboxylic aid is C5-C18 mono or di-carboxylic acid. The carboxylic acid salt (0.001 to 10 wt-%) is dissolved in a water soluble liquid alcohol freezing point depressant such as glycol (90 to 99 wt-%).
U.S. Pat. No. 7,306,750 describes the application of one or a mixture of anhydrous salts, selected from the group consisting of the alkali metal salts, alkali-earth metals salts, amine salts and ammonium salts of C3-C18 mono or di-carboxylic acid for storing the thermal energy where in the temperature range of the thermal energy source is 20 to 180° C.
WO patent 2005/042662 discloses the process for producing a deicing/anti-icing fluid that produces monoalkyl esters of long chain fatty acids. The stream includes water, glycerol, and an alkali containing compounds.
US patent 2003/0015685 discloses low corrosive potassium acetate deicing and anti-icing compositions based on the use of C3-C16 aliphatic monobasic acid or the alkali metal, ammonium or amine salt of monobasic acid as a corrosion inhibitor.
U.S. Pat. No. 7,452,480 relates to carboxylate salts of amines that are used as components of heat exchange fluids. Fluid contains amine carboxylates, preferably triethanolamine formate from 15 to 80 wt-%, and potassium formate up to 50 wt-%.
It would be represent a notable advance in the state of art if one could develop a freezing point depressant which is environmentally benign, but in spite of that biostatic also, non-corrosive and practically immune to salting out and to precipitate formation.
The ideal freezing point depressant composition for airfield pavement deicing, aircraft deicing and anti-icing, heat storage and heat transfer, metal cutting, NOx removal and hydraulic fluid use:                should be free of corrosive halides such as chlorides,        should be free of alkali and alkali-earth metals such as potassium, sodium and calcium,        should not form precipitates on metal surfaces,        should have low toxicity,        should have relatively low biological (BOD) and chemical oxygen demand (COD),        should have reduced electrical conductivity, most preferably below 100 mS/cm,        should be inexpensive to obtain,        and naturally should be effective at low temperatures, i.e. it should have low viscosity and low freezing point, as well as high specific heat capacity and thermal conductivity.        